I seem to recall a more recent Midlands or East Midlands study saying while single car trains are overcrowded on Crewe-Derby services the line doesn't bring in enough revenue to justify 2 car Sprinters on all services. That might mean an extension which brings in extra passengers is the only way of getting the additional revenue needed to strengthen the services.
Two additional diagrams would be needed to extend the Derby service from Crewe to the Airport (approx. 45 minutes each way). Unless the additional farebox revenue exceeded the additional operating costs of the two units and crews, the losses would be even worse!
If EMT keeps the 153s past 2020, the reduced capacity due to the accessible toilet will worsen the overcrowding. A 2-car train might stimulate demand and make on-board ticket checks feasible, so generating more revenue on the existing route.
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I believe the fourth platform was supposed to allow 10tph from the Airport to Piccadilly. The 10 will be 2 North TPE, 1 Scotland, 1 Cleethorpes, 1 Liverpool via CLC, 1 Liverpool via Chat Moss, 1 Cumbria, 1 Blackpool, 1 Bradford and 1 Blackburn - all through services at Picc.
Having now delved into the TSR tables on the
DfT's Northern Franchise Agreement site, I was surprised to find that Northern's required service level from the Airport to Piccadilly actually falls in Dec 2017, from the initial 5tph (same as now plus the remapped TPE Blackpool service) to only 4tph. Then from Dec 2019 it goes back to 5tph, rather than the 6tph I assumed above.
From Dec 2017, the two EMU stoppers to Picc and the Southport DMU service are all withdrawn (it appears the Southport service instead starts from Hebden Bridge via Victoria). The Liverpool via Chat Moss semi-fast EMU is diverted via the CLC and becomes a Northern Connect DMU. The Victoria to Liverpool via Chat Moss EMU stopper starts from the Airport instead (or maybe from Crewe via the Airport). The new Northern Connect DMU service to Barrow/Windermere via Chat Moss and Wigan North Western is inaugurated, with the TPE Glasgow/Edinburghs going back to the Bolton route. Only the ex-TPE Northern Connect Blackpool via Bolton continues as now (but will become EMU assuming the wires are up). One of the Northern Connects (most likely the Blackpool EMU?) will have to be all stations to Piccadilly, in addition to the Liverpool stopper.
From Dec 2019, the additional Airport service is the Northern Connect DMU to Bradford via the Ordsall Chord (this is required to stop at Deansgate).
There is no DfT requirement for the Blackburn via Todmorden Curve service to start from the Airport, so this must be an Arriva proposal that is over and above the agreed requirements. On the other hand, maybe this might mean that the last Airport path is still "up for grabs", with an opportunity for the next Wales and Borders franchisee to bid for it?!